1. Field of the Invention
The present invention relates to a plasma processing apparatus employing the RF induction technique.
2. Description of the Related Art
In semiconductor wafer processing steps, dry etching is performed for, e.g., isolation of capacitors and elements and formation of contact holes. A parallel plate type plasma processing apparatus is known as a representative of conventional apparatuses that perform dry etching, as described in Jpn. Pat. Appln KOKAI Publication No. 61-119686.
In this processing apparatus, a rest table or susceptor serving also as a lower electrode is disposed in an air-tight chamber, and an upper electrode serving also as a gas supply section is disposed above the rest table to oppose it.
In this plasma processing apparatus, first, a semiconductor wafer as an object to be processed is placed on the rest table, and a process gas is supplied from the gas supply section into the chamber. Simultaneously, an RF power is applied across the two electrodes by an RF power supply in order to generate a plasma between these electrodes, thereby etching the wafer by reactive ions in the plasma.
Recently, the line width of patterns of a semiconductor device is more and more decreasing. When a plasma is generated in the above apparatus, the pressure in the chamber is 100 mTorr to 1 Torr. Under this high pressure, since the mean free time of ions is short, micropatterning is difficult to perform. Also, although the diameters of wafers are increasing, when the mean free time of ions is short, a high uniformity of the plasma distribution over a wide surface cannot be ensured, and thus it is difficult to uniformly process a wafer having a large diameter.
For this reason, recently, employment of the RF induction method has been studied. According to this method, as described in European Pat. Appln KOKAI Publication No. 379828 and Jpn. Pat. Appln KOKAI Publication No. 3-79025, the upper wall of the chamber opposing the rest table is constituted by an insulating member, e.g., a quartz glass member, and a flat coil is mounted on the outer surface of the insulating member. An RF current is supplied to this coil to form an electromagnetic field in the chamber. The electrons flowing in the electromagnetic field are caused to collide against neutral particles in the process gas, thereby generating a plasma.
According to this method, a substantially concentric electric field is induced in accordance with the shape of the coil, thereby providing a plasma confining effect. When compared to the conventional parallel plate type plasma processing apparatus, the plasma can be generated with a comparatively low pressure. Accordingly, the mean free time of ions in the generated plasma is long. Therefore, etching by means of this plasma is suitable for micropatterning. The plasma is diffused from a high-density area to a low-density area. Since the mean free time of ions is long, the plasma density distribution is smooth. Thus, the uniformity of the plasma on a plane parallel to the flat surface of the wafer is high, thereby increasing the uniformity within a plane of plasma processing for a wafer having a large diameter.
In this manner, the RF induction method attracts attention as a method suitable for micropatterning and processing of wafers with large diameters. However, this method still has many factors that are yet unknown. Studies are required as to, e.g., how to generate a plasma having a higher density without much increasing the RF power. As a way of generating a high-density plasma, an insulator may be arranged around the wafer, thereby concentrating the plasma. In this case, studies are required as to how to adjust the degree of concentration of the plasma and how to ensure the flatness of the lower surface of the plasma at the peripheral portion of the wafer. The above RF induction method can be realized only after these points are sufficiently studied.